As the cost of classical surgery increases and the sophistication of minimally invasive surgical technology improves, the use of catheters as vehicles for delivering diagnostic and therapeutic agents to internal target sites has similarly increased. Of particular interest herein are catheters which may be used to access target sites through the circulatory system.
There are a number of generalized procedures for placing catheters within vessels in the body for accessing sites that are difficult to approach. Specifically, one such technique involves the use of a torqueable guidewire which, after insertion into the vasculature, is alternately rotated and advanced to the target site. As the guidewire is advanced, the catheter is then tracked along the wire until the distal end of the catheter is also positioned at the desired target site. An early example of this technique is described in U.S. Pat. No. 4,884,579, to Engelson. Although the technology involved in such a catheter is quite sophisticated, many consider an over-the-wire catheter to be a second choice when a highly time-sensitive situation is to be treated and when the vascular site to be accessed is in a path of high blood flow. This is due to the comparatively time-consuming nature of rotating and advancing the guidewire and then advancing the catheter over the guidewire through the vasculature.
An alternative is the use of a flow-directed catheter. One such flow-directed catheter technique includes employing a highly flexible catheter having an inflatable, but pre-punctured, balloon at its distal end. In use, the balloon is partially inflated, and carried by blood flow to the target site. During such a placement procedure, the balloon is continually inflated to replenish fluid leaking from the balloon. This technique, too, has major drawbacks, including the fact that the catheter material is so flexible that the catheter cannot be pushed from the proximal end without buckling some portion of the catheter. Instead, the catheter must be advanced using injected fluid to inflate the balloon in order to propel the catheter to the target site. There is always the risk of rupture of a vessel by a balloon that has been too highly inflated.
Other flow-directed catheters have also been proposed which do not use such leaking balloon technology. Specifically, the catheters are so flexible at their distal and mid regions that they are able to be carried by blood flowing to a target site. Examples of such products are described in U.S. Pat. No. 5,336,205 (to Zenzen et al.) and U.S. Pat. No. 5,538,512 (to Zenzen et al.). These catheters have in common the presence of a relatively stiff tapered proximal segment, a relatively flexible and strong distal segment, and a transition section between those proximal and distal segments which is intermediate in flexibility. The distal segment has a burst pressure release of 195 psi and is made of a material that shows exceptional deflection when a minor force is placed upon such distal portion.
Neither of these patented devices have the structure of the device described below.